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VAI TRÒ CỦA CHỤP CẮT LỚP ĐIỆN KHÁNG TRỞ PHỔI (Electrical Impedance Tomography- EIT) �TRONG HỘI CHỨNG NGUY KỊCH HÔ HẤP CẤP (ARDS)

Ths.BS. Bùi Thị Hạnh Duyên

Trưởng Khoa Hồi sức tích cực-BV ĐHYD.TPHCM

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Nội dung

Mở đầu

Giới thiệu chụp cắt lớp điện kháng trở phổi (EIT)

Vai trò của chụp cắt lớp điện kháng trở phổi trong ARDS

Tóm tắt

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Mở đầu

Mục tiêu quan trọng của quản lý ARDS là thông khí tối ưu đảm bảo oxy hóa đồng thời bảo vệ phổi khỏi tổn thương phổi do máy thở (VILI).
Phương pháp lý tưởng để thực hiện mục tiêu này vẫn chưa được xác định
Chụp cắt lớp điện kháng trở phổi (EIT) có vai trò thế nào trong quản lý thông khí ở BN ARDS.

Rational Use of Intravenous Fluids in Critically Ill Patients. https://doi.org/10.1007/978-3-031-42205-8

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Giới thiệu chụp cắt lớp điện trở kháng phổi (EIT)

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Mở đầu

Chụp cắt lớp điện trở kháng phổi (EIT) cho kết quả hình ảnh về sự thay đổi điện trở kháng trong phổi
Phân biệt các phế nang được thông khí và không được thông khí.
EIT thực hiện tại giường, không xâm lấn và theo thời gian thực

🡪 điều chỉnh kịp thời các thông số thở máy hay tư thế BN

EIT giúp hiểu biết thêm về sinh lý học về thông khí trong tư thế nằm sấp, HFNC, nỗ lực hô hấp và tương tác giữa BN và máy thở

Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Figure 1. Potential clinical applications of electrical impedance tomography: applications of electrical impedance tomographythroughout the course of acute respiratory distress syndrome (ARDS) management. Doted Box: this strategy has been studied in patients undergoing Veno-arterial extracorporeal circulatory support for shock, not in ARDS. *Positive end-expiratory pressure (PEEP) with the lowest degree of overdistension, collapse, homogeneity, and regional compliance. ¶Not yet studied in ARDS. BP = blood

pressure, CoV = center of ventilation, GI = global inhomogeneity, HFNC = high-flow nasal cannula, IMV = invasive mechanical

ventilation, NAVA = neutrally adjusted ventilatory assist, NIV = noninvasive ventilation, ODCL = overdistension/collapse intercept,

PAV+ = proportional assisted ventilation, POCUS = point-of-care ultrasound, PP = prone positioning, P-SILI = patient self-inflicted lung

injury, RV = right ventricle, RVD = regional ventilation delay, SBT = spontaneous breathing trial, VV ECMO = venovenous extracorporeal

membrane oxygenation.

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Nguyên lý hoạt động EIT

Sử dụng 16-32 điện cực để đưa các dòng điện nhỏ vào quanh ngực.
Sự dẫn truyền của những dòng điện này được định lượng để đo điện trở suất của mô.
Điện trở suất mô cao (trở kháng) tạo ra tín hiệu điện thấp và ngược lại

Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Several EIT devices are commercially available (Swisstom BB2 [Swisstom, Landquart, Switzerland],

CareFusion Goe-MF II [CareFusion, H.chberg,

Germany], Timpel Enlight [Timpel, S.o Paulo,

Brazil], Maltron Mark 3.5 [Maltron, Raleigh, United

Kingdom], Dixtal Biomedica Industria [Manaus,

Brazil], Pulmovista 500 [Dr.ger, Lübeck, Germany]),

which use 16–32 electrodes to inject small electrical currents around the chest (Fig. 2). The conduction of these currents is quantified to measure tissue’s resistivity.

High tissue resistivity (impedance) yields a low electrical signal and vice versa (20)

Impedance is determined by the intrinsic properties of the tissue where electricity is applied. The lungs have 80–85% content of air, which acts as an electrical resistor, increasing impedance (18). Conversely, extracellular water serves as a conductor, reducing impedance. These physical properties distinguish between ventilated (high impedance) and nonventilated (low impedance) lungs.

After hundreds of electrical currents are applied and their resistance through tissue is measured, these signals are reconstructed into a digital matrix to generate a cross-sectional map of lung impedance through the respiratory cycle—a ventilation map.

EIT can display a high rate of frames per second, allowing a breath-to-breath ventilation assessment. It can be synchronized with the mechanical ventilator to integrate the preset respiratory cycle and pressures into the matrix (21–23). Ventilator-EIT connectivity varies depending on the manufacturer and might require specific modes of ventilation for accurate measurements

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Nguyên lý hoạt động EIT

Trở kháng được xác định bởi các đặc tính bên trong của mô nơi dòng điện được đưa vào.
Phổi chứa 80–85% không khí, hoạt động như một điện trở: tăng trở kháng
Nước ngoại bào đóng vai trò là chất dẫn điện: giảm trở kháng.
EIT giúp phân biệt giữa phổi được thông khí (trở kháng cao) và phổi không được thông khí (trở kháng thấp).

Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Several EIT devices are commercially available (Swisstom BB2 [Swisstom, Landquart, Switzerland],

CareFusion Goe-MF II [CareFusion, H.chberg,

Germany], Timpel Enlight [Timpel, S.o Paulo,

Brazil], Maltron Mark 3.5 [Maltron, Raleigh, United

Kingdom], Dixtal Biomedica Industria [Manaus,

Brazil], Pulmovista 500 [Dr.ger, Lübeck, Germany]),

which use 16–32 electrodes to inject small electrical currents around the chest (Fig. 2). The conduction of these currents is quantified to measure tissue’s resistivity.

High tissue resistivity (impedance) yields a low electrical signal and vice versa (20)

Impedance is determined by the intrinsic properties of the tissue where electricity is applied. The lungs have 80–85% content of air, which acts as an electrical resistor, increasing impedance (18). Conversely, extracellular water serves as a conductor, reducing impedance. These physical properties distinguish between ventilated (high impedance) and nonventilated (low impedance) lungs.

After hundreds of electrical currents are applied and their resistance through tissue is measured, these signals are reconstructed into a digital matrix to generate a cross-sectional map of lung impedance through the respiratory cycle—a ventilation map.

EIT can display a high rate of frames per second, allowing a breath-to-breath ventilation assessment. It can be synchronized with the mechanical ventilator to integrate the preset respiratory cycle and pressures into the matrix (21–23). Ventilator-EIT connectivity varies depending on the manufacturer and might require specific modes of ventilation for accurate measurements

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Nguyên lý hoạt động EIT

Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Tín hiệu điện trở của dòng điện qua mô, được tái tạo thành ma trận kỹ thuật số
Tạo ra bản đồ cắt ngang về trở kháng của phổi
Tạo ra bản đồ thông khí thông qua chu kỳ hô hấp

Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Several EIT devices are commercially available (Swisstom BB2 [Swisstom, Landquart, Switzerland],

CareFusion Goe-MF II [CareFusion, H.chberg,

Germany], Timpel Enlight [Timpel, S.o Paulo,

Brazil], Maltron Mark 3.5 [Maltron, Raleigh, United

Kingdom], Dixtal Biomedica Industria [Manaus,

Brazil], Pulmovista 500 [Dr.ger, Lübeck, Germany]),

which use 16–32 electrodes to inject small electrical currents around the chest (Fig. 2). The conduction of these currents is quantified to measure tissue’s resistivity.

High tissue resistivity (impedance) yields a low electrical signal and vice versa (20)

Impedance is determined by the intrinsic properties of the tissue where electricity is applied. The lungs have 80–85% content of air, which acts as an electrical resistor, increasing impedance (18). Conversely, extracellular water serves as a conductor, reducing impedance. These physical properties distinguish between ventilated (high impedance) and nonventilated (low impedance) lungs.

After hundreds of electrical currents are applied and their resistance through tissue is measured, these signals are reconstructed into a digital matrix to generate a cross-sectional map of lung impedance through the respiratory cycle—a ventilation map.

EIT can display a high rate of frames per second, allowing a breath-to-breath ventilation assessment. It can be synchronized with the mechanical ventilator to integrate the preset respiratory cycle and pressures into the matrix (21–23). Ventilator-EIT connectivity varies depending on the manufacturer and might require specific modes of ventilation for accurate measurements

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Bachmann et al. Critical Care (2018) 22:263. https://doi.org/10.1186/s13054-018-2195-6

A. Thông khí không đồng nhất: Vùng ngực được thông khí trước sau đó vùng lưng mới được thông khí

B. Thông khí đồng nhất: Vùng ngực và vùng lưng được thông khí đồng thời

Dạng sóng đo thể tích và áp lực đường thở (PAW).

(I) Tăng (PEEP) làm tăng thể tích phổi cuối thì thở ra (ΔEELZ).

(II) Biến đổi theo chu kỳ thông khí (ΔZ) theo dõi những thay đổi về thể tích khí lưu thông (VT).

A.

B

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Bachmann et al. Critical Care (2018) 22:263. https://doi.org/10.1186/s13054-018-2195-6

Không có thông khí ở phổi dưới bên P trong hình ảnh EIT và tình trạng đông đặc tương ứng ở phổi P trên CT ngực

Bản đồ thông khí được chia thành hai vùng quan tâm trong mô hình ARDS, được thông khí với PEEP)=5 cmH2O (trái) và PEEP=15 cmH2O (phải)

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Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Hình 1: thay đổi về trở kháng (trục y) trong suốt giai đoạn giảm dần PEEP (trục x).
Hình 2 (Global ΔZ [Vt]): thay đổi về trở kháng trong quá trình điều chỉnh PEEP: giảm thông khí ở vùng lưng (vùng 4) với PEEP thấp hơn (giảm huy động) .
Hình 3 (ODCL): thay đổi về độ giãn nở phổi qua chỉ số ODCL, tình trạng căng phồng phổi quá mức tăng lên với mức PEEP cao hơn (màu cam ở vùng 1 và 2) và tăng xẹp phổi với mức PEEP thấp hơn (màu xám rõ ràng ở vùng 4).
Hình 4: định lượng mức độ căng phồng phổi (màu cam) và xẹp phổi (màu trắng) với các mức PEEP khác nhau. Khi cả hai đường giao nhau, sẽ đạt được độ xẹp phổi tối thiểu với độ căng phồng phổi tối thiểu (tại chốt màu đỏ). 🡪 PEEP lý tưởng

1

2

3

4

ODCL index: Chỉ số căng phồng phổi và xẹp phổi

Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

1

Chỉ số căng phồng phổi và xẹp phổi (ODCL) ở BN đáp ứng vói PEEP. Biểu đồ trên: những thay đổi về trở kháng (trục y) trong suốt giai đoạn giảm dần PEEP (trục x). Bảng phía trên (Toàn bộ ΔZ [Vt]): những thay đổi về trở kháng trong quá trình điều chỉnh PEEP cho thấy sự mất thông khí ở vùng lưng (vùng 4) với PEEP thấp hơn (giảm huy động) . Bảng dưới (ODCL): khi xem xét các thay đổi về độ giãn nở phổi qua chỉ số ODCL), tình trạng căng phồng phổi quá mức trở nên rõ ràng với mức PEEP cao hơn (màu cam ở vùng 1 và 2). Sự xẹp phổi được ghi nhận với mức PEEP thấp hơn (màu xám rõ ràng ở vùng 4).

Biểu đồ dưới: việc định lượng mức độ căng phồng quá mức (màu cam) và xẹp phổi (màu trắng) được vẽ qua các mức PEEP khác nhau. Khi cả hai đường giao nhau, sẽ đạt được độ xẹp phổi tối thiểu với độ căng phồng phổi tối thiểu (tại chốt màu đỏ). Điều này thể hiện PEEP lý tưởng (trong trường hợp này là PEEP tương đối cao; ở BN có đáp ứng với PEEP) trong đó cả tình trạng căng phồng phổi và xẹp phổi đều được cân bằng.

Figure 3. Overdistension and collapse (ODCL) index in a positive end-expiratory pressure (PEEP) responder. Upper graph: changes in impedance (y-axis) throughout a descending PEEP titration protocol (x-axis). Upper panels (Global ΔZ [tidal volume]): changes in impedance throughout PEEP titration reveal a loss in dorsal ventilation (region 4) with lower PEEP (derecruitment). Lower panels (ODCL): when considering changes in compliance (through the ODCL index), overdistension becomes evident with higher PEEP levels (orange shades in regions 1 and 2). Collapse is noted with lower PEEP levels (clear gray shades in region 4).

Inferior graph: the quantification of overdistension (orange) and collapse (white) is plotted through different PEEP levels. When both lines intercept, the minimum collapse with the minimal overdistension is met (red pin). This represents the ideal PEEP (in this case, a relatively high one; responder) in which both overdistension and collapse are balanced. Image reprinted with permission from Dräger (Lübeck, Germany).

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Vai trò của điện cắt lớp điện kháng trở phổi (EIT) trong ARDS

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Ứng dụng EIT tìm PEEP tối ưu trong ARDS

NC RCT 87 BN ARDS TB- nặng tìm PEEP tối ưu sử dụng EIT vs PV loop
So với nhóm EIT, nhóm PV loop có

PEEP cao hơn (17,4 ±1,7 vs 16,2±2,6 cmH2O, p=0,02).
Sau 48 giờ, driving pressure cao hơn (12,4 ± 3,6 vs 10,9 ± 2,5 cmH2O, p=0,04).

Tỷ lệ sống thấp hơn (44,4% vs 69,0%, p=0,02; HR 2,1; KTC 1·1–3,9)
Có thể có bị nhiễu do sử dụng ECMO nhiều hơn ở nhóm EIT và tần số thở nhanh hơn ở nhóm PV loop🡪 mechanical power cao hơn.

Hui-Ju Hsu et al Physiol. Meas. 42 (2021) 014002

Physiol. Meas. 42 (2021) 014002

Abstract

Objective. The aim of the study was to compare titration of positive end-expiratory pressure (PEEP) with electrical impedance tomography (EIT) and with ventilator-embedded pressure–volume (PV) loop in moderate to severe acute respiratory distress syndrome (ARDS). Approach. Eighty-seven moderate to severe ARDS patients (arterial oxygen partial pressure to fractional inspired oxygen ratio, PaO2/FiO2�200 mmHg) were randomized to either EIT group (n=42) or PV group (n=45). All patients received identical medical care using the same general support guidelines and protective mechanical ventilation. In the EIT group, the selected PEEP equaled the airway pressure at the intercept between cumulated collapse and overdistension percentages curves and in the PV group, at the pressure where maximal hysteresis was reached. Main results. Baseline characteristics and settings were comparable between the groups. After optimization, PEEP was significantly higher in the PV group (17.4±1.7 versus 16.2±2.6 cmH2O, PV versus EIT groups, p=0.02). After 48 h, driving pressure was significantly higher in the PV group (12.4±3.6 versus 10.9±2.5 cmH2O, p=0.04). Lung mechanics and oxygenation were better in the EIT group but did not statistically differ between the groups. The survival rate was lower in the PV group (44.4% versus 69.0%, p=0.02; hazard ratio 2.1, confidence interval 1·1–3.9). None of the other pre-specified exploratory clinical endpoints were significantly different. Significance. In moderate to severe ARDS, PEEP titration guided with EIT, compared with PV curve, might be associated with improved driving pressure and survival rate.

Trial registration: NCT03112512, 13 April, 2017.

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Ứng dụng EIT tìm PEEP tối ưu trong ARDS

NC RCT 117 BN ARDS, sử dụng EIT vs bảng PEEP/FiO2
Không có sự khác biệt đáng kể về

Tỷ lệ tử vong (21% vs 27%, p = 0,63),
Thời gian nằm ICU (13,0 (7,0-25,0) vs 10,0 (7,0, -14,8), p = 0,17)
Số ngày không thở máy vào ngày thứ 28 (14,0 (2,0, 23,0) vs 19,0 (0,0, 24,0), p = 0,55)
Không có chấn thương khí áp mới.
So với nhóm chứng, ΔD1-SOFA và ΔD2-SOFA thấp hơn đáng kể trong nhóm EIT
Tuy nhiên, NC bao gồm ARDS nhẹ (32,5 %) 🡪 ảnh hưởng tiên lượng.

He et al. Crit Care (2021) 25:230

Abstract

Background: Individualized positive end-expiratory pressure (PEEP) by electrical impedance tomography (EIT) has

potential interest in the optimization of ventilation distribution in acute respiratory distress syndrome (ARDS). The aim

of the study was to determine whether early individualized titration of PEEP with EIT improved outcomes in patients

with ARDS.

Methods: A total of 117 ARDS patients receiving mechanical ventilation were randomly assigned to EIT group

(n = 61, PEEP adjusted based on ventilation distribution) or control group (n = 56, low PEEP/FiO2 table). The primary outcome was 28-day mortality. Secondary and exploratory outcomes were ventilator-free days, length of ICU stay, incidence of pneumothorax and barotrauma, and difference in Sequential Organ Failure Assessment (SOFA) score at day 1 (ΔD1-SOFA) and day 2 (ΔD2-SOFA) compared with baseline.

Measurements and main results: There was no statistical difference in the value of PEEP between the EIT group

and control group, but the combination of PEEP and FiO2 was different between groups. In the control group, a

significantly positive correlation was found between the PEEP value and the corresponding FiO2

(r = 0.47, p < 0.00001) since a given matched table was used for PEEP settings. Diverse combinations of PEEP and FiO2 were found in the EIT group (r = 0.05, p = 0.68). There was no significant difference in mortality rate (21% vs. 27%, EIT vs. control, p = 0.63), ICU length of stay (13.0 (7.0, 25.0) vs 10.0 (7.0, 14.8), median (25th–75th percentile); p = 0.17), and ventilator-free days at day 28 (14.0 (2.0, 23.0) vs 19.0 (0.0, 24.0), p = 0.55) between the two groups. The incidence of new barotrauma was zero. Compared with control group, significantly lower ΔD1-SOFA and ΔD2-SOFA were found in the EIT group

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Ứng dụng EIT tìm PEEP tối ưu trong ARDS

20 BN ARDS
NC thử nghiệm chéo so sánh giữa chỉnh PEEP bằng EIT và PEEP đo bằng áp lực thực quản xuyên phổi
Không có sự khác nhau PEEP giữa 2 nhóm
Nhưng PEEP theo từng cá nhân thì không tương đồng giữa 2 phương pháp
, PEEP_EIT có liên quan đến sự phân bổ thông khí đồng nhất hơn so với PEEP_PL.
Phân tích dưới nhóm ARDS tại phổi và ngoài phổi, sử dụng EIT có PEEP thấp hơn ở ARDS tại phổi và cao hơn ở ARDS ngoài phổi.

Scaramuzzo et al, Critical Care Medicine 48(8):p 1148-1156, August 2020. DOI: 10.1097/CCM.0000000000004439

Figure 2. Correlation and Bland-Altmann plot between the levels of positive end-expiratory pressure (PEEP)

determined by electrical impedance tomography (EIT) and transpulmonary pressure measurements. A, Spearman

correlation between the levels of PEEP set based on EIT and on transpulmonary pressure. B, Bland-Altman plot

plotting the difference between the two methods versus the mean values of both methods.

Objectives: Different techniques exist to select personalized positive

end-expiratory pressure in patients affected by the acute

respiratory distress syndrome. The positive end-expiratory transpulmonary

pressure strategy aims to counteract dorsal lung collapse,

whereas electrical impedance tomography could guide

positive end-expiratory pressure selection based on optimal homogeneity

of ventilation distribution. We compared the physiologic

effects of positive end-expiratory pressure guided by electrical impedance

tomography versus transpulmonary pressure in patients

affected by acute respiratory distress syndrome.

Design: Cross-over prospective physiologic study.

Setting: Two academic ICUs.

Patients: Twenty ICU patients affected by acute respiratory distress

syndrome undergoing mechanical ventilation.

Intervention: Patients monitored by an esophageal catheter and a

32-electrode electrical impedance tomography monitor underwent

two positive end-expiratory pressure titration trials by randomized

cross-over design to find the level of positive end-expiratory pressure

associated with: 1) positive end-expiratory transpulmonary

pressure (PEEPPL) and 2) proportion of poorly or nonventilated

lung units (Silent Spaces) less than or equal to 15% (PEEPEIT).

Each positive end-expiratory pressure level was maintained for 20

minutes, and afterward, lung mechanics, gas exchange, and electrical

impedance tomography data were collected.

Measurements and Main Results: PEEPEIT and PEEPPL differed

in all patients, and there was no correlation between the

levels identified by the two methods (Rs = 0.25; p = 0.29).

PEEPEIT determined a more homogeneous distribution of ventilation

with a lower percentage of dependent Silent Spaces

(p = 0.02), whereas PEEPPL was characterized by lower airway—

but not transpulmonary—driving pressure (p = 0.04). PEEPEIT was

significantly higher than PEEPPL in subjects with extrapulmonary

acute respiratory distress syndrome (p = 0.006), whereas the opposite

was true for pulmonary acute respiratory distress syndrome

(p = 0.03).

Conclusions: Personalized positive end-expiratory pressure levels

selected by electrical impedance tomography– and transpulmonary

pressure–based methods are not correlated at the individual

patient level. PEEPPL is associated with lower dynamic stress,

whereas PEEPEIT may help to optimize lung recruitment and homogeneity

of ventilation. The underlying etiology of acute respiratory

distress syndrome could deeply influence results from each

method. (Crit Care Med 2020; 48:1148–1156)

Key Words: acute respiratory distress syndrome; electrical

impedance tomography; positive end-expiratory pressure;

precision medicine; transpulmonary pressure

Results

We enrolled 20 patients (13 males and seven females) of

61 years old (52–71 yr old) with a median BMI of 28 kg/m2

(24–33 kg/m2) and a Pao2/Fio2 of 149 (96–211). Ten were classified

as ARDSp and 10 as ARDSexp. Patient characteristics at

enrollment are reported in Table 1.

Median values of set PEEPEIT and PEEPPL were respectively

14 cm H2O (8–17 cm H2O) and 13 cm H2O (11–15 cm H2O)

with an intraindividual difference of 1.5 cm H2O (–7.0 to

5.8 cm H2O) (Fig. 1) (p = 0.95). However, individual values of

PEEPEIT and PEEPPL selected in each patient were different, and

the correlation between them was not significant (Rs = 0.25;

p = 0.29) (Fig. 2A). Bland-Altman analysis showed a bias of

0.2 cm H2O with wide LOAs between 12.0 and –11.6 cm H2O

(Fig. 2B). Although PEEPPL was associated with significantly

slightly lower respiratory system driving pressure (11.2 cm

H2O [9–13.8 cm H2O] vs 9.8 cm H2O [8.4–13 cm H2O];

p = 0.04), the transpulmonary driving pressure was not significantly

different among the two methods (7 [5–10.1] vs 6.9

[4.8–8.8]; p = 0.13) (Table 2). At the regional level, PEEPEIT

was associated with more homogeneous distribution of ventilation

compared with PEEPPL. Comparing the DfV in each step

with the hypothetical value of 50%, we found no significant

difference in the PEEPEIT step (48.3% [34.9–52.4%]; p = 0.11),

whereas the opposite was true in the PEEPPL one (41.5% [39.1–

51.6%]; p = 0.005) (Fig. S1, Supplemental Digital Content 1,

http://links.lww.com/CCM/F573). The same was found

analyzing the RCRATIO, which differed significantly from 1 in the PEEPPL step (0.7 [0.64–1.07]; p = 0.009) (Fig. S1, Supplemental

Digital Content 1, http://links.lww.com/CCM/F573; legend,

Supplemental Digital Content 4, http://links.lww.com/CCM/

F576) but not in the PEEPEIT one (0.93 [0.54–1.01]; p = 0.19).

Moreover, PEEPEIT provided significantly lower values of Sstot (11.3% [9.6–13.8%] vs 16% [10–21%]; p = 0.02), primarily

because of lower SSdep (8 [6.4–11] vs 12 [7.7–18]; p = 0.02)

(Table 2 and Fig. 1). Hemodynamics and gas exchange did

not differ between the two PEEP levels (Table 2). Powerrs calculated

during each study step was not statistically different

(p = 0.2) and correlated significantly (Rs = 0.78; p < 0.01) (Fig.

S2, Supplemental Digital Content 2, http://links.lww.com/

CCM/F574; legend, Supplemental Digital Content 4, http://

links.lww.com/CCM/F576).

The results of the titration techniques in ARDSp versus

ARDSexp are reported in Table 3. In ARDSp, PEEPEIT suggested

a lower value of PEEP compared with the PL technique

(PEEPEIT = 9 cm H2O [5–15 cm H2O]; PEEPPL = 14 cm H2O

[12–15 cm H2O]; p = 0.03), resulting in a significantly lower

end-inspiratory PL (5.7 cm H2O [4.2–9.5 cm H2O] vs 8 cm H2O

[5.7–12.2 cm H2O]; p = 0.04) and a more homogeneous distribution

of ventilation (COVVD: PEEPEIT = 50.4% [42.5–53%];

PEEPPL = 51% [46.4–53%]; p = 0.04).

In ARDSexp, PEEPEIT suggested a higher value of PEEP

(PEEPEIT = 14 cm H2O [13–20 cm H2O]; PEEPPL = 11 cm H2O

[7–14 cm H2O]; p = 0.006), resulting in a better ventrodorsal

(COVVD: PEEPEIT = 49.7% [48.1–54.4%]; PEEPPL = 46% [42.2–

48.2%]; p = 0.002) and right-left (COVRL: PEEPEIT = 39.7%

[35.6–45.1%]; PEEPPL = 37.9% [31.3–42.3%]; p = 0.004) ventilation

distribution, a lower value of SStot (PEEPEIT = 11.8

[10–13.9]; PEEPPL = 19.2% [15.2–25.2%]; p = 0.002) but a

slightly higher respiratory system and transpulmonary driving

pressures (Table 3; and Fig. S3, Supplemental Digital Content

3, http://links.lww.com/CCM/F575; legend, Supplemental

Digital Content 4, http://links.lww.com/CCM/F576).

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Ứng dụng EIT trong thông khí tư thế nằm sấp (TKNS)

TKNS vs thông khí nằm ngửa (TKNN)

Làm tăng Vt, thông khí các vùng phụ thuộc (Vtdep), 🡪 cải thiện thông khí đồng nhất (Hom) (1,1±0,9 vs 1,7±0,9, P=0,021).
TKNS cũng giảm ODCL index (19±9% vs 28±8%, P=0,005)
TKSN tăng V phổi có thể huy động được (80 [71-157] vs 59 [1-110] ml, P=0,025).
“Khả năng bảo vệ phổi” của TKNS được dự đoán bởi Vtdep thấp hơn, Vtndep cao hơn và Hom kém hơn được đo ở tư thế nằm ngửa cơ bản (P<0,05).

Minerva anestesiol 2020;86:1057-64. Doi: 10.23736/s0375-9393.20.14130-0)

Hom= Vtndep/Vtdep, với tỷ lệ 1 tương ứng với sự thông khí đồng nhất hoàn hảo

Minerva anestesiol 2020;86:1057-64. Doi: 10.23736/s0375-9393.20.14130-0)

Vtndep/Vtdep ratio, with ratio of 1 cor- responding to perfect ventilation homogeneity

Hom=Vtdep/

EIT cho phép đánh giá linh hoạt tại giường về tác dụng sinh lý của TKNS và có thể hỗ trợ nhận biết sớm những bệnh nhân ARDS có nhiều khả năng được hưởng lợi từ TKSN hơn.

BacKgroUND: Prone position (PP) improves acute respiratory distress syndrome (arDs) survival by reducing the risk of ventilation-induced lung injury. However, inter-individual variability is a hallmark of arDs and lung protection by PP might not be optimal in all patients. in the present study, we dynamically assessed physiologic effects of PP by electrical impedance tomography (EIT) and identified predictors of improved lung protection by PP in ARDS patients. MetHoDs: Prospective physiologic study on 16 intubated, sedated and paralyzed patients with arDs undergoing PP as per clinical decision. eit data were recorded during two consecutive steps: 1) baseline supine position before and after a recruitment maneuver (RM); 2) prone position before and after a RM. “Improved lung protection” by PP was defined in the presence of simultaneous improvement of ventilation homogeneity (Hom), alveolar overdistension and collapse (oDcl) and amount of recruitable lung volume by rM in comparison to supine.

resUlts:

PP versus supine increased the tidal volume distending the dependent regions (Vtdep), resulting in improved Hom (1.1±0.9 vs. 1.7±0.9, P=0.021). PP also reduced oDcl (19±9% vs. 28±8%, P=0.005) and increased the recruitable lung volume (80 [71-157] vs. 59 [1-110] ml, P=0.025). “improved lung protection” by PP was predicted by lower Vtdep, higher Vtndep and poorer Hom measured during baseline supine position (P<0.05).

coNclUsioNs: eit enables dynamic bedside assessment of the physiologic effects of PP and might support early recognition of ARDS patients more likely to benefit from PP.

(Cite this article as: Dalla corte F, Mauri t, spinelli e, lazzeri M, turrini c, albanese M, et al. Dynamic bedside assessment of the physiologic effects of prone position in acute respiratory distress syndrome patients by electrical impedance tomogra- phy. Minerva anestesiol 2020;86:1057-64. Doi: 10.23736/s0375-9393.20.14130-0)

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Nghiên cứu 21 BN ARDS TB- nặng do COVID-19 thở máy sử dung EIT và Ctscan để đánh giá thông khí phổi khi TKNS

Critical Care Medicine 50(5):p 723-732, May 2022. | DOI: 10.1097/CCM.0000000000005450

Bản đồ thông khí (màu xanh) tưới máu (màu đỏ)

Bảng đồ thông khí (màu xanh) tưới máu (màu đỏ)

Nghiên cứu BN ARDS TB- nặng do COVDI-19 thở máy sử dung EIT và Ctscan để đánh giá thông khí phổi khi TKNS

Critical Care Medicine 50(5):p 723-732, May 2022. | DOI: 10.1097/CCM.0000000000005450

Figure 1. Recruitment measured by CT scan expressed as % of total lung weight and Electrical impedance tomography-based timeimpedance curve (TIC) concavity index in the supine and prone position. Recruitment induced by the prone position was significant at the global level (A), but ventral lung regions were characterized by derecruitment (B) and only dorsal lung was recruited (C). The TIC concavity index improved at the global and dorsal regional level (D and F) without worsening in the ventral derecruited region (E). Red bars represent mean values. *p < 0.01 versus supine. ns = not significant

Figure 2. Effects of prone position on recruitment and ventilation-perfusion matching in a representative study patient. Top: CT scan images performed in the supine (left) and prone position (right). Note the recruitment in the dorsal regions and the derecruitment in the ventral part of the right lung. Bottom: Electrical impedance tomography assessment of ventilation (blue) and perfusion (red). Note the large fraction of only-ventilated units (dead space) in the ventral lung regions during supine position (left), largely decreased by prone position (right); only perfused units (shunt), instead, increased in the same ventral region.

OBJECTIVES: Prone positioning allows to improve oxygenation and decrease

mortality rate in COVID-19–associated acute respiratory distress syndrome

(C-ARDS). However, the mechanisms leading to these effects are not fully understood.

The aim of this study is to assess the physiologic effects of pronation by the

means of CT scan and electrical impedance tomography (EIT).

DESIGN: Experimental, physiologic study.

SETTING: Patients were enrolled from October 2020 to March 2021 in an Italian

dedicated COVID-19 ICU.

PATIENTS: Twenty-one intubated patients with moderate or severe C-ARDS.

INTERVENTIONS: First, patients were transported to the CT scan facility, and

image acquisition was performed in prone, then supine position. Back to the ICU,

gas exchange, respiratory mechanics, and ventilation and perfusion EIT-based

analysis were provided toward the end of two 30 minutes steps (e.g., in supine,

then prone position).

MEASUREMENTS AND MAIN RESULTS: Prone position induced recruitment

in the dorsal part of the lungs (12.5% ± 8.0%; p < 0.001 from baseline) and derecruitment

in the ventral regions (–6.9% ± 5.2%; p < 0.001). These changes led to a

global increase in recruitment (6.0% ± 6.7%; p < 0.001). Respiratory system compliance

did not change with prone position (45 ± 15 vs 45 ± 18 mL/cm H2O in supine

and prone position, respectively; p = 0.957) suggesting a decrease in atelectrauma.

This hypothesis was supported by the decrease of a time-impedance curve concavity

index designed as a surrogate for atelectrauma (1.41 ± 0.16 vs 1.30 ± 0.16;

p = 0.001). Dead space measured by EIT was reduced in the ventral regions of the

lungs, and the dead-space/shunt ratio decreased significantly (5.1 [2.3–23.4] vs 4.3

[0.7–6.8]; p = 0.035), showing an improvement in ventilation-perfusion matching.

CONCLUSIONS: Several changes are associated with prone position in

C-ARDS: increased lung recruitment, decreased atelectrauma, and improved

ventilation-perfusion matching. These physiologic effects may be associated with

more protective ventilation.

KEY WORDS: atelectrauma; electrical impedance tomography; prone position;

pulmonary perfusion; recruitmen

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Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Figure 1. Potential clinical applications of electrical impedance tomography: applications of electrical impedance tomography

throughout the course of acute respiratory distress syndrome (ARDS) management. Doted Box: this strategy has been studied in

patients undergoing Veno-arterial extracorporeal circulatory support for shock, not in ARDS. *Positive end-expiratory pressure (PEEP)

with the lowest degree of overdistension, collapse, homogeneity, and regional compliance. ¶Not yet studied in ARDS. BP = blood

pressure, CoV = center of ventilation, GI = global inhomogeneity, HFNC = high-flow nasal cannula, IMV = invasive mechanical

ventilation, NAVA = neutrally adjusted ventilatory assist, NIV = noninvasive ventilation, ODCL = overdistension/collapse intercept,

PAV+ = proportional assisted ventilation, POCUS = point-of-care ultrasound, PP = prone positioning, P-SILI = patient self-inflicted lung

injury, RV = right ventricle, RVD = regional ventilation delay, SBT = spontaneous breathing trial, VV ECMO = venovenous extracorporeal

membrane oxygenation.

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Một số lưu ý và giới hạn

Thiếu chuẩn hóa các kết cục và các mục tiêu: nên các nghiên cứu thử nghiệm về EIT có thể kém đồng nhất cho phân tích và so sánh
Thường các nghiên cứu EIT có thời gian <24h
Giới hạn độ sâu <40mm🡪 việc sử dụng EIT BN beó phì kém tin cậy
Vị trí đặt đai điện cực quan trọng và sự so sánh các lần khác nhau cần cùng vị trí đặt đai điện cực

Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Although multiple parameters and indexes have been proven effective in assessing ventilation distribution and the amount of collapse/overdistension, there is controversy regarding the ideal one.

Lack of standardization in outcomes and target values might render the ongoing EIT trials too heterogeneous for analysis and comparisons.

Most EIT studies have focused on short-term physiologic effects. Little is known beyond the initial 24 hours. Although EIT was validated in the setting of perioperative management of obese patients (114), the measurements are limited in depth (<40 mm) (115), making them less reliable in this population.

Proper placement of the belt is essential, as caudal placement increases the possibility of measuring diaphragmatic excursion in the frame (116). Similarly, as body positioning (lateral, prone, or the angle inclination of the bed) (56, 117) influences the mechanical properties of the lung (118), it can also modify tidal impedance distribution and variability. Therefore, when an intervention is being assessed (e.g., PEEP titration), the evaluation of impedance changes must be in the same position pre- and post interventions.

Respiratory effort might modify the transpleural pressures and, therefore, tidal and end-expiratory

volume/impedance independently from PEEP changes. Ideally, PEEP titration should be done in a

passively breathing patient. Changes in lung composition, such as those occurring during rapid fluid bolus administration, can decrease lung impedance (119).

The potential of interfering with pacemakers and other thoracic implantable electrical devices and the

risk of inducing skin lesions limits its use in specific populations (burns).

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Tóm tắt

EIT là công cụ hứa hẹn nhiều hữu ích cho BN ARDS

Tìm PEEP tối ưu
Đánh giá thông khí ở BN ARDS: căng phồng phổi và xẹp phổi, đồng nhất trong thông khí
Thông khí và tưới máu
Hiệu quả của thông khí nằm sấp
Đáng giá các hiệu quả can thiệp trên BN ARDS

EIT là thiết bị giúp đo đạc theo dõi tại giường, trong thời gian thực
Cần thêm các nghiên cứu về hiệu quả và giảm tử vong khi ứng dung EIT trên BN ARDS

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Chân thành cảm ơn quý thầy cô và đồng nghiệp đã chú ý lắng nghe

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Jose Victor Jimenez et al, August 2022 • Volume 50 • Number 8. DOI: 10.1097/CCM.0000000000005582

Figure 4. Overdistension and collapse (ODCL) index in a positive end-expiratory pressure (PEEP) nonresponder: upper graph: changes in impedance (y-axis) throughout a descending PEEP titration protocol (x-axis). Upper panels (Global ΔZ [tidal volume]): changes in impedance throughout PEEP titration have no significant impact on ventilation with lower PEEP. Lower panels (ODCL): when considering changes in compliance (through the ODCL index), overdistension becomes evident with higher PEEP (orange shades in regions 1–4) and progressively diminishes (particularly in ventral regions 1–2) with lower PEEP. Note that collapse is minimum with lower PEEP. Inferior graph: the quantification of overdistension (orange) and collapse (white) is plotted through different PEEP levels. Lower levels of overdistension (orange numbers) and collapse (white numbers) are met with a PEEP of 9 cm H2O (?🡪 6 mới đúng). Image reprinted with permission from Dräger (Lübeck, Germany).